Reactors for use in vehicles such as hybrid vehicles have a structure in which a magnetic gap having a predetermined width is formed between a plurality of core materials in order to prevent a reduction in inductance. More specifically, an integral core, which is formed by inserting a spacer such as ceramic or the like into a gap portion between each pair of core materials, and bonding the core material and the spacer which are adjacent to each other together using an adhesive, is used.
FIG. 9 is a schematic view for explaining an example conventional reactor and a method of manufacture thereof. Specifically, between a core material 12 having a predetermined thickness and having an arc shape or a substantially U-shape (hereinafter referred to as a “U core material”) and a core material 14 having the same thickness as the U core material 12 and having a column shape or a substantially I-shape (hereinafter referred to as an “I core material”), a spacer 16 having the same thickness as the U core material 12 and the I core material 14 is inserted (see FIG. 9(a)).
The spacer 16 is bonded to each of the U core material 12 and the I core material 14 by using an adhesive, to thereby form a core assembly 18 having a substantially J-shape (hereinafter referred to as a “J core assembly). After coil bobbins 20a and 21b are formed on the J core assembly 18, a coil 48a is disposed or wound over the outer peripheral surface of the coil bobbin 20a to form a J core member 24 (see FIG. 9(b)).
A J core member 44 having the same shape as that of the J core member 24 is formed in the same manner as the J core member 24. Then, the J core member 24 and the J core member 44 are arranged such that an end surface 13 of the U core material 12 and an end surface 15 of the I core material 14 of the J core member 24 face an end surface 35 of an I core material 34 and an end surface 33 of a U core material 32 of the J core member 44, respectively (see FIG. 9(c)).
The J core members 24 and 44 are then bonded to each other via spacers 22 and 42 by using an adhesive, so that a reactor 50 including an annular core 46 formed of a plurality of core materials coupled with each other via the spacers, and coils 48a and 48b provided on the outer peripheral surfaces of the coil bobbins 20 and 21, respectively, is obtained (see FIG. 9(d)). It should be noted that FIG. 9 illustrates the structure of the coil bobbins 20 and 21 (in FIGS. 9(b) and 20a, 20b, 21a, and 21b in FIG. 9(c)) and the coils 48a and 48b provided on the outer peripheral surface of the core 46 only in a schematic cross section, in order to show the detailed structure of the adhesion surfaces between the core materials and the spacer and the vicinity thereof.
Conventionally, a powder magnetic core, a laminated steel sheet composed of a plurality of electromagnetic steel sheets, and so on have been used as a core material for a reactor. In recent years, with an increasing demand for a further reduction in costs in hybrid vehicles on which a reactor is mounted and so on, a powder magnetic core is preferably used as a core material from the viewpoint of reduction in the material costs and the manufacturing costs. The powder magnetic core as used herein is manufactured using soft magnetic powders having a particle size of about 100 μm, for example, in such a manner that after processing the powder surfaces with insulation treatment using an insulating material, a binder is added as necessary, and the powders are subjected to pressure forming and further subjected to baking or thermal treatment, as required.
The powder magnetic core generally exhibits a lower Young's modulus than the laminated steel sheet, and therefore a reactor in which the powder magnetic core is used is subjected to effects of an electromagnetic attractive force in the adhesion direction between the core material and the spacer, which may result in generation of a large amount of vibration. Generation of vibration as described above may further lead to disadvantages including generation of noise and peeling of at least a part of the adhesion surface between the core material and the gap plate.
JP 2006-135018 A describes that, in a core of a reactor in which a laminated steel sheet is used, a gap spacer includes a projection portion, on a surface of the gap spacer to be bonded to a core material, which comes into contact with the core material, so that a space to be filled with an adhesive is provided between the gap spacer and the core material to thereby ensure the spreading area and the thickness of the adhesive, thereby preventing peeling of the adhesion portion and also suppressing a noise generated by the reactor.
The invention described in the above-described in JP 2006-135018 A may show excellent advantages when a certain degree of mechanical strength of the core material itself is ensured, such as when a laminated steel sheet is employed, for example. However, particularly when a powder magnetic core is applied as the core material, the mechanical strength of the core material itself is generally lower than the core material in which a laminated steel sheet or the like is applied, and at the time of handling, such as mounting of a reactor and so on, and particularly during travelling of a vehicle in which such a reactor is mounted, the core material may suffer from deficiencies caused by vibration or the like. It is therefore preferable that the strength of the core material itself is reinforced simultaneously with reinforcement of the adhesion performance between the core material, formed of a powder magnetic core, and the spacer.
Here, while it is possible to reinforce the mechanical strength of the powder magnetic core which is used as the core material to a certain degree by increasing the amount of binder, an increase in the amount of binder may degrade other desirable material characteristics such as magnetic permeability. It is therefore very difficult to maintain these material characteristics in a desirable state while adjusting the amount of binder. Also, because desirable material characteristics as a core material vary depending on the case in which the core material is actually used, it is very difficult and impractical to prepare core materials having various material characteristics and at the same time to increase the strength of the core material itself.